Police are appealing for witnesses or anyone with information to come forward following the death of a motorcyclist in St Marys early yesterday (Saturday).

Emergency services attended a motorcycle crash at Mamre Road, St Marys, near the intersection of Hall Street at about 2.45am.

The rider, a man believed to be aged in his 40s, was treated at the scene by NSW Ambulance paramedics, however, he died at the scene.

Nepean Police Area Command is investigating the incident and a report will be prepared for the Coroner.

Anyone with any information is urged to contact Crime Stoppers on 1800 333 000.